This application claims the priority of Korean Patent Application No. 10-2004-0006459, filed on Jan. 31, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a compensation of an error in a hard disk drive, and more particularly, to a method and apparatus for high-speed compensation of a repeatable run-out (RRO) error in a hard disk drive.
2. Description of the Related Art
Recently, a storage density of a hard disk drive has rapidly increased due to the development of magneto-resistive head techniques. There has been proposed, for example, a product capable of storing 80 GByte of data per disk, of which a track density is 93,000 TPI (tracks per inch) and a track width is 0.27 μm. A new product capable of storing 120 GByte of data per disk is expected to be developed soon. In a technique for precisely controlling a head position, it is required that the head precisely writes/reads data in/from such a fine track.
To accurately control the head position in the hard disk drive, the head must quickly move to a target track and be positioned over a center of the target track even, if there is an error. If an external shock is applied to the hard disk drive or a fastening state of a disk is not perfect during a manufacturing process thereof, a repeatable run-out (RRO) error appears, by which a track center of the disk is offset from a rotation center of the disk. The RRO error deteriorates a controlling performance of the head position. In particular, the RRO is severely generated when an offline servo writing method is used to implement servo writing to the disk before the disk is fastened to the hard disk drive. For example, when a hard disk drive having a track density of 93,000 TPI is assembled using the offline servo writing method, an RRO error of above 200 tracks is expected. It is necessary to compensate the excessive RRO error, since this remarkably deteriorates the performance of the hard disk drive at high operating speeds.
FIG. 1 is a block diagram of a conventional apparatus for compensating the RRO error in a hard disk drive. Referring to FIG. 1, an RRO compensator 110 is connected in parallel to a state feedback controller 130 to compensate the RRO error. The RRO compensator 110 is a secondary filter having an infinite gain at an RRO frequency, and a position error signal (PES) converges to zero, after a predetermined time. In order to improve a convergence speed of the RRO compensator 110, the RRO compensator is initialized to a value of a normal state when the compensator starts operating. A period of time of above 20 msec is required until the compensation is implemented, because of mutual interference of the RRO compensator 110 and the state feedback controller 130. Therefore, there is a problem in that the performance of the hard disk drive is significantly deteriorated.